Professor Les Ebdon, director of the Office for Fair Access (Offa), said tutors were tempted to select students from “good middle-class” homes because they were less likely to drop out.

The Headmasters’ and Headmistresses’ Conference of leading independent schools said the comments were “disappointing” and “insensitive” to thousands of sixth-formers awaiting their A-level results this week.

Prof Ebdon suggested that payments to universities to take more students from poor backgrounds must be protected from government cuts.

“There may well be additional costs for taking on students from disadvantaged backgrounds,” he said.

“To put it bluntly, if you really want to maximise the income of your university, then you take kids from a good middle-class background whose parents can ensure they don't fall into financial difficulty.”

He said the £327million student opportunity fund, which is facing 10 per cent cuts, was vital to compensate universities that do offer places to students who are disadvantaged.

However, Chris Ramsay, a universities spokesman for the HMC, which represents 250 leading independent schools, said there was no evidence that universities were biased in favour of middle-class candidates.

Mr Ramsay, headmaster of the King's School Chester, said: “It is disappointing to read yet again of a senior commentator accusing universities of social bias.

“The only pressure we can see being brought to bear on universities is from pressure groups who would like them to discriminate against ‘middle class’ applicants, which at the moment they are rightly resisting.”

He said universities must not be expected to manipulate their admissions to fit a social agenda.

“It is for schools to encourage aspiration. Aspiration cannot be tacked on to teenagers' educational experience through quangos,” he said.

“Above all, to accuse universities of bias in admissions is scaremongering. It is inappropriate and insensitive of the director of Offa to be making such accusations, especially days before thousands of sixth formers will be hearing about their own futures.”

Ministers have encouraged universities to offer more places to working class students from less successful schools.

Tutors have been told to take account of students’ backgrounds and offer places to candidates with potential from disadvantaged schools on the basis of lower A-level results than those achieved by privately-educated pupils.